The P-38 can opener is a small device found in a C-ration which (keychain sized) consists of a short metal blade that serves as a handle (and a screwdriver to the resourceful), with a small, hinged metal tooth that folds out to pierce the can lid. A notch just under the hinge point keeps the opener hooked around the rim of the can as the device is "walked" around to cut the lid out. A larger version called the P-51 is somewhat easier to operate.
A similar device is currently employed by the Australian Army in its ration kits. It is known by the acronym "FRED" (Fucking Ridiculous Eating Device)
